In the semiconductor industry, the minimum feature sizes of microelectronic devices are well into the deep sub-micron regime to meet the demand for faster and lower power semiconductor devices. The downscaling of complimentary metal-oxide-semiconductor (CMOS) devices imposes scaling constraints on the gate dielectric material where the thickness of the conventional SiO2 gate dielectric is approaching its physical limits. To maintain the projected performance enhancement from one generation of devices to the next, to improve device reliability and to reduce electrical leakage from the gate dielectric to the transistor channel during operation of the device, semiconductor transistor technology requires dielectric materials with a higher dielectric constant than that of SiO2, and that allow increased physical thickness of the gate dielectric layer while maintaining a low equivalent oxide thickness (EOT).
Low temperature processing of semiconductors is of interest for the downscaling of future ultra large scale integration (ULSI) semiconductor devices. Plasma oxidation and nitridation, utilizing oxygen and nitrogen plasma, is a promising low temperature technique to form oxynitride gate dielectric films, buried oxynitride layers or germanium/silicon on insulator (GOI/SOI) structures, or nitrided dielectric layers on floating gates. While formation of nitrided dielectric layers by plasma processing has been reported, little details on the active plasma species have been disclosed, including how plasma sources and plasma processing conditions may be chosen to select plasma species that form the desired nitrided dielectric layers.
Silicon (Si) oxynitride layers are viewed as one of the most promising alternate materials to replace the SiO2 gate oxide, while still being compatible with the Si technology. Thin oxynitride layers are usually formed either by thermal processing methods or by plasma based methods. Nitriding ultra-thin oxide layers to form oxynitride layers, has been shown to alleviate various limitations encountered with oxide layers. The improvements include increased resistance to boron penetration, lower tunneling leakage current and interface-state generation, and less threshold voltage shift under constant current conditions. The improved dielectric properties that are observed for oxynitride layers are attributed to the fact that the nitrogen atoms at the surface of the SiO2/Si act as a barrier to boron penetration and can reduce strain at the SiO2/Si interface.
In addition to Si based MOS technology, germanium (Ge) based MOS technology is a likely candidate for future CMOS technology, including the 22 nm technology node and beyond, because of its high carrier mobility, small band gap for voltage scaling, and high solubility of p-type dopants. In order to integrate Ge based technology into semiconductor devices, for example gate stacks, it may be necessary to form a high quality passivation layer on the Ge surface to improve interface characteristics and to avoid intermixing of Ge and the gate dielectric film.
Germanium oxynitride layers may contain GeO2, which is thermally unstable and water soluble. Since wafers go through several wet chemical treatments during a manufacturing process, the presence of GeO2 can affect the properties of the integrated germanium oxynitride layers. Thus, processing methods are needed that allow formation of a germanium oxynitride layer with a selected chemical bonding environment (e.g., GeO2 vs GeO), in addition to tunable nitrogen concentration and control of the layer thickness.